With the view of reducing the emission of carbon dioxide gas which is known as a major cause of global warming, there is a growing movement to use hydrogen gas that contains no carbon instead of hydrocarbons such as petroleum. In the field of transportation, extensive research efforts have been directed to hydrogen vehicles that directly burn hydrogen gas and fuel cell vehicles using fuel cells. Fixed fuel cells for cogeneration purposes are also being actively developed.
Hydrogen gas can be produced by the reforming of hydrocarbons and the electrolysis of water. Steam reforming is one of possible reforming processes, and produces hydrogen and carbon monoxide by causing a reaction between steam and hydrocarbons such as natural gas and naphtha at a high temperature in the presence of a catalyst. See Patent Document 1, for instance. The carbon monoxide obtained by the steam reforming is caused to react with water in a water gas shift reaction, thereby producing hydrogen and carbon dioxide gases.
When hydrogen gas is produced by reforming hydrocarbons, carbon dioxide is inevitably produced as a byproduct. Therefore, in order to prevent the carbon dioxide from being released to the atmosphere and avoid contributing to global warming, the carbon dioxide gas is required to be separated from the hydrogen gas, and stored in an appropriate manner. As a method for removing carbon dioxide gas from any gas, it is known to cause the gas containing the carbon dioxide gas to contact an absorption liquid such as alkanolamine water solution that absorbs carbon dioxide, and to be absorbed therein. See Patent Document 2, for instance. The absorption liquid that has absorbed carbon dioxide releases the carbon dioxide gas by means of a regeneration process consisting of a heating process. The regenerated absorption liquid can be recycled to be used once again. By using this method, carbon dioxide gas can be separated from the hydrogen gas. The separated carbon dioxide can be prevented from being released to the atmosphere, for instance, by being stored underground or under the sea. By thus recovering and storing (CCS) the carbon dioxide gas, the hydrogen gas can be utilized as clean energy that does not produce carbon dioxide even during the production process.